Free Money Boost at Game Start:
Start a new game then win the race. After you win go to the first toilet
that you encounter and save your game. Now, go to the main menu and select
START GAME and then select RESTART STORY. DO NOT skip the cutscene. You
will keep the money and PP that you earned after winning the race
($10,000 for first place) and repeat this as many times as you like.